The present invention relates to voltage-converting battery modules, and to portable systems which include them.
Background: Battery Management
Currently the custom solutions to applications of rechargeable energy services are costly and inflexible. Chargers must be custom designed and cannot be interchanged. Batteries are unique for each application and have very unique charge and discharge characteristics. Complex algorithms are often used for charge/discharge control.
Recently some efforts have been made to standardize batteries, but they still require custom, highly specialized interface electronics. (Examples include the DuraCell PowerSmart.TM. battery models DR35 and DR121, Motorola battery models EP3656, and Molicell model ME202.) Even the "standards" that are being proposed are too unique and specialized, and require highly specialized interface electronics.
Background: Smart Battery Modules
In the 1990s some battery modules have included logic chips (either microcontrollers or programmed custom logic chips). These chips are used for charge/discharge control, communications, and related functions such as overtemperature and overcurrent monitoring, or for a "gas gauge" function which estimates battery life.
Background: Converting Battery Modules
A further development was introduced in the Fall of 1996 (less than one year before the effective filing date of the present application), when Compaq Computer Corporation shipped a battery module which included an integral DC-DC switching converter. The DC-DC converter provided precise regulation of the charging voltage applied to lithium-ion battery cells, and hence permitted lithium-ion compatibility to be retrofitted into a system which was not originally designed for it. (Specifically, this battery module was used with a system where the voltage regulation from the AC adapter was not precise enough to be a safe supply for charging lithium-ion batteries.)
Universal Battery Module
The present invention provides a new battery pack architecture which contains several new concepts. This battery pack contains an integral converter, so that the voltage of the battery cells does not have to match the voltage of the system power lines at all. In the presently preferred embodiment, the converter is bidirectional, and can increase or decrease the voltage in either direction.
If conventional power bus voltages and battery cell configurations are used, the integral converter can be operated as a buck converter when the battery is charging (to efficiently change the system voltage to match the battery's preferred charging voltage), and as a boost converter when the battery is discharging, to increase the battery voltage to the exact value required by the system. However, the battery voltage does not have to be less than the system voltage, but can alternatively be greater (if the converter is programmed to achieve this). Moreover, the voltage conversion ratios do not have to be constant. Thus, the charge and discharge curves can be fully optimized for the exact characteristics of the particular battery being used. This permits greater efficiency of energy extraction from a given battery, and this in turn translates to greater energy density in the battery. This is one of the key goals of battery development for portable computers.
This architecture provides many advantages, including at least the following:
Complete and simple programmability of battery charge and discharge voltage curves. This permits total optimization of the battery's energy storage and lifetime. PA0 The universal battery module can charge from a very wide range of sources, and has no special requirements for the charging source at all. PA0 The universal battery module preferably provides automatic and simple conversion between discharge and charge mode. PA0 The universal battery module is chemistry independent. The system does not need to know the detailed optimization of each new battery technology introduced, and hence battery technology can be updated as fast as practical.
A particular advantage of this power architecture is that the system can use a really poor quality AC adapter, since the converting battery module is more tolerant of voltage irregularities on the system power bus. Moreover, the converting battery module can even compensate for short drop-outs in the power-line voltage during AC operation. For example, when a nearby motor starts up, the voltage at an AC power line outlet might drop, for example, from 115 V to 100 V for a few hundred milliseconds. With such a sag in power-line voltage, the DC output from a low-quality AC adapter might drop, for example, from 40 volts to 35 volts (or less). However, if a fully-charged converting battery module is present on the computer's power bus, and has its voltage regulation setpoint at 39 V, then the battery module will keep the system power voltage from falling below 39 V during the power glitch (without any switching or delay for decisionmaking). This adds stability to the system operation. (Similarly, the same battery module can be used to perform the same function in another system which has a different bus voltage.)
A converting battery module means that a detachable battery module has the capability to provide power directly into a system bus. This permits the electronics on the system side to be simplified. Moreover, a single battery module can be used on systems with different voltage requirements (as long as the output voltage is appropriately programmed).
A particular advantage of the systems which include a converting battery module is that the circuitry on the system side can be simplified. The battery module itself can be made quite indifferent to voltage fluctuations on the system power bus, so that the specifications on the AC adapter can be anything which is acceptable to the devices which operate in the system. Moreover, charge can also be drawn from other sources, such as a telephone wall jack or a car battery.
A smart battery module typically includes a microcontroller, and some form of digital communication is preferably provided between the battery module's microcontroller and control components on the system side. However, an advantage of the universal battery module is that it can be used for simpler electronic systems, as well as for powering computers. Thus, manufacturers may wish to bring out simple components, such as a portable game machine, portable audio playback device, camcorder, flashlight, radio-controlled toy, or power tool, which is powered by the same high-end batteries which are used to power computers or high-end telecommunications equipment. The universal battery module described in the present application can power this wide variety of equipment, even if their power requirements are widely different.
As noted above, the use of an integral bidirectional up/down converter in the battery module permits the battery voltage to be higher than the system voltage. In one notable class of embodiments, the voltage across the electrochemical cells is intentionally made higher than the system power embodiments. This is particularly advantageous with chemistries which operate most efficiently at relatively low current. This also permits the individual battery cells to be electrically connected in a purely series configuration, rather than the series-parallel configurations which are more common. A pure series configuration guarantees that all cells will have transferred equal amounts of charge, whereas parallel or series-parallel configurations do not guarantee this. With standard cells, this embodiment permits designers to pick a convenient standard cell size, pick a number of cells to achieve the required power and energy, and then combine them in series without worrying about the voltage of the combined cells.